THE good bacteria in our bodies wage war on disease and keep us healthy. Here's how to keep that tiny army strong...

We are each home to about 100 trillion bacteria, “good” and “bad”. While most of us are aware the bad bacteria can cause illness, scientists are increasingly realising that the friendly or good bacteria help to keep us well.

Early last century Russian scientist Dr Ilya Mechnikov speculated that certain “toxic” bacteria in the gut aggravated the ageing process.

The solution to the problem, he found, was drinking fermented milk, which increased lactic acid bacteria in the gut and prevented the bad bugs multiplying and causing damage.

Despite forming the basis for today’s billion-pound industry of probiotic drinks and yogurts, for decades Mechnikov’s theory went unnoticed by the wider scientific community. The exception was Japanese scientist Minoru Shirota, who was inspired by Mechnikov’s work.

He went on to develop a strain of lactic acid bacteria which he used to make the fermented milk drink Yakult, the first bottle of which was produced in 1935, although it didn’t reach the UK until 1996.

Indeed the notion that good bacteria play a key role in keeping us healthy didn’t attract much attention until the 1990s but has since gained momentum at a dramatic pace.

In 2007 a major US initiative called the Human Microbiome Project (HMP) set about mapping each individual bacterium, including where it lives in the body, to determine its role in human health and disease. Although the pioneering scientists acknowledge there’s still a lot they don’t yet know they’ve been piecing the puzzle together ever since the project began.

The implication of the findings to date is that bacteria, which live on our skin and in our noses, mouths, urogenital tracts and intestines, have a huge impact on our overall health and wellbeing.

But while we can’t change our inherited genes we can change our personal microbiome – for better and for worse.

A Moroccan spicy bean soup with chickpeas and coriander is great news for your gut [GETTY ]

HOW HEALTHY MICROBES KEEP US WELL

They banish “bad” microbes. Imagine the inside wall of your lower digestive tract is a kerb lined with parking spaces.

All microbes compete for these spaces but it’s the healthy microbes that once in stay put. Healthy microbes make lactic acid and fatty acids, which lower the pH inside the colon to a level where unwanted yeasts and bacteria can’t thrive.

They attack infections. When we have a virus our healthy microbes spring into action, stopping the virus from multiplying and counteracting any toxins it makes.

Our ancestors ate a lot of fermented foods

They aid digestion. Healthy microbes help the body to digest carbohydrates. Any carbs such as fibre that can’t be digested become food for bacteria in the large intestine.

They make vitamins. Food is the main provider of vitamins but the healthy microbes in our body make some too, such as certain B vitamins and vitamin K.

HOW DO I LOOK AFTER MY MICROBIOME?

Eat a healthy, balanced diet. It seems the proportion of carbohydrate and fat in our diet may affect the balance of bacteria in our gut, although more research is needed to identify how and why this is.

Nevertheless, a diet that’s healthiest for our body is likely to be healthiest for the good bacteria in our gut too. Base meals on unrefined carbs and keep fat intake, especially saturated fats, down.

Increase your high-fibre foods. Because fibre, which the body can’t digest, ends up in the large intestine where it feeds bacteria it’s important to get enough.

A lack of fibre in our diet means the good bugs go hungry so are unable to flourish and work at their best.

The easy solution is to eat plenty of high-fibre foods such as vegetables, fruit, nuts, seeds, chickpeas, beans, lentils and wholegrains, including oats and brown rice.

Read all about the wonders of your gut and how to keep it strong in this months Healthy Food Guide [HANDOUT]

Have probiotic yogurts or drinks, or take a supplement. Probiotics are gut-friendly strains of bacteria that improve the quality and diversity of our microbiome.

There are many probiotic yogurts and drinks available such as Yakult, Actimel, Activia and Müller Vitality as well as a variety of probiotic supplements.

Include fermented foods. Our ancestors ate a lot of fermented foods, mainly because the fermentation process helps to preserve perishables.

Each nationality has its own traditional recipes. Koreans eat pickled vegetables or kimchi; Germans eat sauerkraut, pictured above; Turks eat kefir; Japanese use miso and many Europeans eat yogurt.

Research shows that fermented foods are also natural sources of probiotics or good bacteria.

WHAT CONDITIONS MIGHT BE IMPROVED BY A DAILY DOSE OF PROBIOTICS?

Gastrointestinal infections and diarrhoea. The strongest evidence for taking probiotics to improve health is linked to their role in preventing and treating diarrhoea.

In a review of 63 studies probiotics taken with rehydration powders were found to reduce the frequency and duration of diarrhoea. If you suffer a bout of gastroenteritis take probiotics daily for about a month.

Irritable bowel syndrome (IBS). It is estimated that between 10 and 20 per cent of adults in the UK suffer with IBS, which can develop after a bout of gastroenteritis.

The main symptoms are bloating, stomach cramps, flatulence, diarrhoea and constipation.

In many IBS sufferers the microbiome is out of balance so restoring the microbiota (gut flora) can help to relieve uncomfortable symptoms.

A review of 14 trials at the University of Oxford found probiotics played a role in alleviating some of the symptoms of IBS, including pain, flatulence and bloating.

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Lactose intolerance. This condition occurs when the body is unable to digest lactose, the main sugar in milk. It is caused by a lack of the enzyme lactase which breaks down lactose.

It is often a temporary condition, occurring after a stomach bug that resulted in diarrhoea.

Symptoms include bloating, cramping, loose stools and flatulence. Research shows that lactobacillus acidophilus helps to produce the enzyme lactase and so aid digestion and absorption of lactose. Try Quest Acidophilus Plus, £8.89 for 60 capsules.

Inflammatory bowel disease. According to a review of 41 studies there is not yet enough evidence to support the use of probiotics in Crohn’s disease. But their use looks far more promising for people with ulcerative colitis.

Constipation. A change in bacteria in the gut can have the unwelcome effect of slowing movement in the bowel.

A review of 11 trials found taking probiotic supplements reduced the amount of time it took for food to pass through the digestive tract with the greatest effects seen in older adults and those who were constipated.

Bifidobacterium lactis strains seemed to have the greatest effect.

Coughs, colds and infections. Around 70 per cent of our immune system is in our digestive system and taking probiotics has been linked with a lower incidence of coughs, colds and infections.

Chinese researchers looked at 10 different studies and found people taking probiotics had a reduced incidence of upper respiratory tract infections compared with those taking a placebo. They were also less likely to need antibiotics.

Obesity. Emerging research suggests there is a link between the balance of microbes in our gut and our weight.

Much of the work is still in its early stages but studies show obese people tend to have a poor-quality microbiome compared with slim people.

We don’t yet know whether this is a cause or consequence of obesity but studies do show weight loss or weight gain can affect the balance and composition of gut bacteria.

The full version of this feature is in the August issue of Healthy Food Guide magazine, on sale now. For more nutrition advice and recipes visit healthyfood.co.uk